Method for sealing pipelines using a gel pig

ABSTRACT

The present invention provides methods and methods for curing a leakage in a pipeline, the method including at least one gel pig and at least one sealant composition; wherein the at least one gel pig and the at least one sealant composition form a pig train, adapted to move along the pipeline to a region of the leakage and to seal the leakage.

FIELD OF THE INVENTION

The present invention relates generally to gel pigs for use in pipelinesand methods for producing them, and more specifically to methods andapparatus for use in water pipelines.

BACKGROUND OF THE INVENTION

Many liquids are transported via subterranean/underwater pipelines. Whena leakage crack or hole forms in the pipeline, the liquid leakstherefrom. Often, it takes a long time to detect a leakage and yetlonger to locate the leakage site. Oil, gas and water transportation arethus subject to tremendous losses due to pipeline leakage.

There is thus a need to maintain and seal subterranean/underwaterpipelines quickly in situ.

Several patent publications in the field include U.S. Pat. No.3,523,826A which relates to a process for cleaning a piping system whichis characterized by circulating in, and through said system athixotropic emulsion having a hi.-h volume ratio of internal phase toexternal phase, the emulsion having an emulsifying agent, anemulsifiable oil and a non-oil, the emulsion being an oil-in-non-oil ora non-oil-in-oil emulsion, the internal phase of said emulsion beingpresent in said emulsion in an amount of at least 80% by volume of theemulsion, said emulsion having the characteristics of a solid when atrest and the characteristics of a liquid when a force is exerted on it,said emulsion tending to be non-adhesive, said emulsion having acritical shear point sufficient to permit pumping at high rates, andsaid emulsion having an apparent rest viscosity greater than about 1000cps.

U.S. Pat. No. 4,216,026 describes a method for removing fluid and/orparticulate debris from a pipeline, a Bingham plastic fluid plug ispassed through a pipeline and the fluid and/or debris are collected bythe plug. The plug is pushed through the pipeline with a scraper whichin turn may be pushed by liquid or gas pressure. Where the fluid to beremoved is water, the Bingham plastic fluid plug employed preferably isa composition of water and a xanthan gum, and the gum may becross-linked with a multivalent metal. Where the fluid to be removed isa hydrocarbon, the Bingham plastic fluid plug employed preferably is acomposition of a mineral oil and an organo-modified smectite, and mayalso include a particulate filler such as powdered coal.

U.S. Pat. No. 4,252,465A describes a gel plug, which is employed duringconstruction of an offshore pipeline to separate a gas-filled portion ofthe pipeline from a water-flooded portion, and to facilitate control andmovement of the gas/gel plug/water interface as desired to assist inconstruction operations.

U.S. Pat. No. 4,254,559A relates to an interior surface of a pipelinebeing dried by sequentially passing through the pipeline (a) an aqueouscross-linked gelled pig, (b) a fluid mobility buffer comprising anon-cross-linked gelled ankanol of from one to three carbon atoms, (c) adessicating amount of a liquid alkanol from one to three carbon atoms.For example, a pipeline was dried by sequentially passing through it (a)a borate cross-linked hydroxypropyl guar gum pig, (b) a fluid mobilitybuffer comprising methanol thickened with hydroxypropyl cellulose, and(c) methanol.

U.S. Pat. No. 4,379,722 discloses a gel plug of mineral oil,organo-modified smectite, and a particulate filler such as powderedcoal, or a gel plug of mineral oil and organo-modified smectite isemployed during construction of an off-shore pipeline to separate agas-filled portion of the pipeline from a water-flooded portion, and tofacilitate control and movement of a gas/gel plug/water interface asdesired to assist in construction operations.

U.S. Pat. No. 4,416,703 describes a method to remove particulate debrisfrom a pipeline, a plug train including at least one gel plug havingdebris entraining characteristics and at least one pseudoplastic plug ispassed through a pipeline and the debris is collected by the gel plug.The gel plug is pushed through the pipeline with a scraper which in turnmay be pushed by liquid or gas pressure.

U.S. Pat. No. 4,321,968A discloses gelled compositions comprisingcarboxymethylhydroxyethyl cellulose in aqueous brine solutions, whichare gelled by the addition of an alkaline earth metal hydroxide such ascalcium hydroxide. The gelled compositions have utility as waterdiversion agents, pusher fluids, fracturing fluids, drilling muds,work-over fluids, and completion fluids.

U.S. Pat. No. 5,346,339A provides a method of cleaning a pipeline usinga gel pig of a graft copolymer of a hydroxyalkyl cellulose prepared by aredox reaction with vinyl phosphonic acid. The gel pig is formed byhydrating the graft copolymer in an aqueous liquid. The gel pig iscrosslinked by the addition of a Lewis base or Bronsted-Lowry base, tothe gel in an amount sufficient to initiate crosslinking of the graftcopolymer. Contaminants entrained in the crosslinked gel pig during thecleaning process may be separated by the addition of a pH reducing agentto the pig whereby the viscosity of the gel is caused to decrease. Thegel may be used for further cleaning after contaminant separation byaddition of an additional quantity of the Lewis base or Bronsted-Lowrybase.

US2003109385A provides a process for treating a hydrocarbon-bearingformation having at least one hydrocarbon bearing zone and at least onewater bearing zone wherein the ratio of the permeability of thehydrocarbon bearing zone(s) to the permeability of the water bearingzone(s) is in the range of from 1:20 to 3:1 comprising: a) sequentiallyinjecting into the formation: (i) an aqueous polymer solution comprising0.01 to 0.5 weight percent of a water-soluble polymer having from 0.01to 7.5 mole percent of crosslinkable carboxylate and/or phosphonategroups and a molecular weight in the range of 250,000 to 12,000,000; and(ii) an aqueous solution of a crosslinking agent; and b) back-producingthe aqueous polymer solution over the crosslinking agent so that thepolymer crosslinks within the formation to form a gel which iscollapsible to allow hydrocarbon flow.

US2008277112A discloses a method for treating a portion of asubterranean formation or a propellant pack is provided. In general, themethod comprises the steps of: (A) forming or providing a treatmentfluid comprising: (i) water; (ii) a chelating agent capable of forming aheterocyclic ring that contains a metal ion attached to at least twononmetal ions; and (iii) a viscosity-increasing agent; and (B)introducing the treatment fluid into the wellbore under sufficientpressure to force the treatment fluid into the matrix of the formationor the propellant pack.

WO2008081441 describes a method of repairing leakage in pipelinescomprising the steps of forming a first and second openings in thepipeline upstream and downstream, respectively, of the leakage location,inserting through the first opening a first body, filling the spacearrear of the first body (C1) with a first viscous sealing material(M1), inserting through the first opening a second body (C2) arrear ofthe first viscous sealing material (M1) compressing the first sealingmaterial by applying a pressure against the first and the second bodies(C1, C2) in opposite directions, causing the first and second bodies(C1, C2) and the compressed first sealing material (M1) to move inunison in the direction of the second opening, and retrieving the firstand second bodies (C1, C2). Preferably, the method is performed usingthree bodies (C1, C2, C3) and two sealing materials (M1, M2).

However, there are still many types of pipeline leakages, which cannotbe cured using the aforementioned prior art materials and methods. Therethus remains an urgent need to develop systems and methods for curingpipeline leakages.

SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to providemethods of forming gel pigs for use in systems and methods for sealingpipeline leakages.

In preferred embodiments of the present invention, improved methods areprovided for producing gel pigs.

In other embodiments of the present invention, a method and system areprovided for sealing leaks in water transport pipelines.

There is thus provided according to an embodiment of the presentinvention, a method for curing at one leakage site in a pipeline, themethod including

-   -   a. introducing a pig train into the pipeline, the pig train        including;        -   i) at least one gel pig; and        -   ii) at least one sealant composition; wherein the at least            one gel pig and the at least one sealant composition form            said pig train;    -   b. enabling the pig train to move along the pipeline to a region        of the at least one leakage and to seal the at least one        leakage.

Additionally, according to an embodiment of the present invention, theat least one gel pig includes one gel pig and the at least one sealantcomposition includes one sealant composition.

Moreover, according to an embodiment of the present invention, the atleast one gel pig includes two gel pigs and the at least one sealantcomposition includes one sealant composition.

Further, according to an embodiment of the present invention, the atleast one gel pig includes three gel pigs and the at least one sealantcomposition includes two sealant compositions.

Yet further, according to an embodiment of the present invention, thepig train moves along the pipeline at a speed of 0.01 to 10 m/s.

Furthermore, according to an embodiment of the present invention, the atleast one gel pig includes one rear pig.

Additionally, according to an embodiment of the present invention, atleast one of the two pigs has an average diameter of at least 5% lessthan an internal diameter of the pipeline.

Moreover, according to an embodiment of the present invention, at leastone of the two pigs has an average diameter of at least 10% less than aninternal diameter of the pipeline.

Importantly, according to an embodiment of the present invention, the atleast one gel pig includes;

-   -   a. a cellulosic polysaccharide;    -   b. a surfactant; and    -   c. water.

Additionally, according to an embodiment of the present invention, theat least one gel pig further includes;

-   -   d. a filler; and    -   e. a metallic hydroxide.

According to another embodiment of the present invention, the at leastone gel pig further includes an oil.

Moreover, according to an embodiment of the present invention, the atleast one gel pig includes a rear pig and a front pig of differentcompositions.

Furthermore, according to an embodiment of the present invention,wherein the pig train conforms to an inner profile of the pipeline.

Additionally, according to an embodiment of the present invention, theinner profile of the pipeline is reduced in diameter in at least onesection by at least 20%.

Further, according to an embodiment of the present invention, the innerprofile of the pipeline is reduced in diameter in at least one sectionby at least 50%.

Yet further, according to an embodiment of the present invention, theinner profile of the pipeline is reduced in diameter in at least onesection by at least 75%.

Additionally, according to an embodiment of the present invention, theinner profile of the pipeline is further increased in the diameter in atleast one section by at least 20%.

Moreover, according to an embodiment of the present invention, the innerprofile of the pipeline is increased in the diameter in at least onesection by at least 50%.

Additionally, according to an embodiment of the present invention, theinner profile of the pipeline is increased in the diameter in at leastone section by at least 75%.

Furthermore, according to an embodiment of the present invention, themethod further includes propelling a pressurized fluid from a first endthereof along the pipeline.

Additionally, according to an embodiment of the present invention, thepressurized fluid includes a liquid.

Moreover, according to an embodiment of the present invention, thepressurized fluid includes a gas.

Further, according to an embodiment of the present invention, hepressurized fluid includes a tri-phase fluid.

Yet further, according to an embodiment of the present invention, thepressurized fluid is at a pressure of 1-150 bar.

Additionally, according to an embodiment of the present invention, thepig train prevents a bypass of a propelling product by of more than 30%.

Moreover, according to an embodiment of the present invention, themethod further includes extracting the pig train from the pipeline via aconduit of less than two inch diameter at a pressure of less than 3 bar.

Furthermore, according to an embodiment of the present invention, themethod further includes introducing or launching the pig train into thepipeline via a conduit of less than two inch diameter at a pressure ofless than 5 bars.

Additionally, according to an embodiment of the present invention, themethod further includes counter-pressurizing the pig train from a secondend of the pipeline with a counter pressurized fluid.

Further, according to an embodiment of the present invention, thecounter pressurized fluid is for controlling velocity of movement of thepig train along the pipeline.

Yet further, according to an embodiment of the present invention, thepig train is launched from a pipe of a diameter of less than 75% of thepipeline.

Additionally, according to an embodiment of the present invention, thepig train is launched from a pipe of a diameter of less than 50% of thepipeline.

In some cases, according to an embodiment of the present invention thepig train is launched from a pipe of a diameter of less than 75% of thepipeline.

Additionally, according to an embodiment of the present invention, thepig train is launched from a pipe at an angle of greater than 30° to thepipeline.

Furthermore, according to an embodiment of the present invention, thepig train is launched from a pipe at an angle of greater than 60° to thepipeline.

In some cases, according to an embodiment of the present invention, thepig train is launched from a pipe at an angle of greater than 80° to thepipeline.

Additionally, according to an embodiment of the present invention, thepig train is launched from a pipe at a pressure in the range of 2-15bar.

Further, according to an embodiment of the present invention, the pigtrain is launched from a pipe at a pressure in the range of 2-5 bar.

Importantly, according to an embodiment of the present invention, thepig train travels through an obstruction in the pipeline and isoperative thereafter.

Additionally, according to an embodiment of the present invention, theobstruction is selected from the group consisting of a butterfly valve,a wedge, a nail, a screw, an obstructing element, an in-pipe meter, aservice pipe ferrule, an incrustation and a tuberculation, a baffle, abroomstick seal and combinations thereof.

The present invention provides systems and methods for curing a leakagein a pipeline, the system including at least one gel pig and at leastone sealant composition; wherein the at least one gel pig and the atleast one sealant composition form a pig train, adapted to move alongthe pipeline to a region of the leakage and to seal the leakage.

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in connection with certain preferredembodiments with reference to the following illustrative figures so thatit may be more fully understood.

With specific reference now to the figures in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

In the drawings:

FIG. 1A is a simplified pictorial illustration showing a system forsealing a pipeline, in accordance with an embodiment of the presentinvention;

FIG. 1B is a simplified pictorial illustration showing another systemfor sealing a pipeline, in accordance with an embodiment of the presentinvention;

FIG. 1C is a simplified pictorial illustration showing another systemfor sealing a pipeline, in accordance with an embodiment of the presentinvention;

FIG. 1D is a simplified pictorial illustration showing another systemfor sealing a pipeline, in accordance with an embodiment of the presentinvention;

FIG. 2 is a simplified flow chart of a method for sealing a pipeline, inaccordance with an embodiment of the present invention;

FIG. 3 is a simplified flow chart of another method for sealing apipeline, in accordance with an embodiment of the present invention;

FIG. 4 is a simplified flow chart of another method for sealing apipeline, in accordance with an embodiment of the present invention; and

FIG. 5 is a simplified pictorial illustration showing a system forsealing a pipeline, in accordance with an embodiment of the presentinvention.

In all the figures similar reference numerals identify similar parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the detailed description, numerous specific details are set forth inorder to provide a thorough understanding of the invention. However, itwill be understood by those skilled in the art that these are specificembodiments and that the present invention may be practiced also indifferent ways that embody the characterizing features of the inventionas described and claimed herein.

Reference is now made to FIG. 1A, which is a simplified pictorialillustration showing a system 100 for sealing a pipeline, in accordancewith an embodiment of the present invention.

System 100 is constructed and configured to seal a pipeline 106comprising at least one leakage site 108, such as a crack or hole.System 100 comprises a sealant composition 102 and a gel pig 104. System100 is adapted to travel along the pipeline using a first pressure force110 to the rear of the gel pig and a counter force 112 upstream (lesserthan force 110). Some non-limiting examples of the gel pig compositionsappear in the examples hereinbelow. Some non-limiting examples of thesealant compositions are disclosed in Israel Patent No. 180474.

A non-limiting example of composition 104 is:

-   -   a) At least one organic or inorganic filler selected from carbon        ash, aluminum hydroxide, calcium carbonate, calcium hydroxide,        magnesium hydroxide, magnesium carbonate, titanium hydroxide,        silica, similar fillers and combinations thereof in a weight        ratio of 0.01-3% wt/wt.    -   b) At least one gelling agent selected from carrageenan, agar        agar, hydroxymethylcelluose, hydroxyethyl cellulose,        hydroxypropyl cellulose and combinations thereof in a weight        ratio of 0 to 20% wt/wt.    -   c) A coloring agent selected from a water soluble dye, a water        insoluble dye, a paint, an oxide, a metal oxide and combinations        thereof in a weight ratio of 0 to 1% wt/wt.    -   d) At least one surfactant selected from an ionic surfactant, an        anionic surfactant, a detergent, an edible oil, an inedible oil        and combinations thereof in a weight ratio of 0.01 to 10% wt/wt.    -   e) At least one aqueous agent selected from sea water, tap        water, distilled water, ice and combinations thereof in a weight        ratio of 20 to 90% wt/wt.

FIG. 1B shows a simplified pictorial illustration showing another system120 for sealing a pipeline, in accordance with an embodiment of thepresent invention. System 120 comprises two gel pigs 104, 106. These gelpigs may be of identical or different compositions. These are termedherein a rear gel pig 104 and a front gel pig 106. Dispersed between thetwo gel pigs is sealant composition 102. Some non-limiting examples ofthe gel pig compositions appear in the examples hereinbelow. Somenon-limiting examples of the sealant compositions are disclosed inIsrael Patent No. 180474.

There can be seen in FIG. 1C a simplified pictorial illustration showinganother system 140 for sealing a pipeline, in accordance with anembodiment of the present invention. System 140 comprises three gel pigs104, 114, 118 and two sealant compositions 102, 116. These gel pigs maybe of identical or different compositions. Likewise, sealantcompositions 102, 116 may be identical or different. Some non-limitingexamples of the gel pig compositions appear in the examples hereinbelow.Some non-limiting examples of the sealant compositions are disclosed inIsrael Patent No. 180474.

A non-limiting example of composition 114 is:

-   -   a) At least one organic or inorganic filler selected from carbon        ash, aluminum hydroxide, calcium carbonate, calcium hydroxide,        magnesium hydroxide, magnesium carbonate, titanium hydroxide,        silica, similar fillers and combinations thereof in a weight        ratio of 0.01-10% wt/wt.    -   b) At least one gelling agent selected from carrageenan, agar        agar, hydroxymethylcelluose, hydroxyethyl cellulose,        hydroxypropyl cellulose and combinations thereof in a weight        ratio of 0 to 30% wt/wt.    -   c) A coloring agent selected from a water soluble dye, a water        insoluble dye, a paint, an oxide, a metal oxide and combinations        thereof in a weight ratio of 0 to 1% wt/wt.    -   d) At least one surfactant selected from an ionic surfactant, an        anionic surfactant, a detergent, an edible oil, an inedible oil        and combinations thereof in a weight ratio of 0.01 to 20% wt/wt.    -   e) At least one aqueous agent selected from sea water, tap        water, distilled water, ice and combinations thereof in a weight        ratio of 20 to 85% wt/wt.

A non-limiting example of composition 118 is:

-   -   a) At least one organic or inorganic filler selected from carbon        ash, aluminum hydroxide, calcium carbonate, calcium hydroxide,        magnesium hydroxide, magnesium carbonate, titanium hydroxide,        silica, similar fillers and combinations thereof in a weight        ratio of 0.01-10% wt/wt.    -   b) At least one gelling agent selected from carrageenan, agar        agar, hydroxymethylcelluose, hydroxyethyl cellulose,        hydroxypropyl cellulose and combinations thereof in a weight        ratio of 0 to 30% wt/wt.    -   c) A coloring agent selected from a water soluble dye, a water        insoluble dye, a paint, an oxide, a metal oxide and combinations        thereof in a weight ratio of 0 to 1% wt/wt.    -   d) At least one surfactant selected from an ionic surfactant, an        anionic surfactant, a detergent, an edible oil, an inedible oil        and combinations thereof in a weight ratio of 0.01 to 20% wt/wt.    -   e) At least one aqueous agent selected from sea water, tap        water, distilled water, ice and combinations thereof in a weight        ratio of 20 to 85% wt/wt.

FIG. 1D is a simplified pictorial illustration showing another method160 for sealing a pipeline, in accordance with an embodiment of thepresent invention. Method 160 comprises two gel pigs 114, 170 and asealant composition 102 or 116 disposed therebetween. The front gel pig114 may be similar or identical to those described herein. The rear gelpig 170 comprises at least two or three different compositions 122, 124,126, for introduction into a pipeline sequentially (first 122, then 124and thereafter 126).

Additionally or alternatively, the rear gel pig comprises fourcompositions, five compositions, six compositions, seven compositions,eight compositions or another multiplicity of compositions. A fourthcomposition 128 (not shown), a fifth composition 130 (not shown), asixth composition 132 (not shown).

Additionally or alternatively, the rear gel pig comprises fourcompositions, five compositions, six compositions, seven compositions,eight compositions or another multiplicity of compositions. A fourthcomposition 128 (not shown), a fifth composition 130 (not shown), asixth composition 132 (not shown).

When six compositions are applied, the first composition (front to back)serves as a separator between the sealing composition and the secondcomposition. It has a density of 1.0-1.5 g/cm³. The second composition,together with the third composition, forms a two (horizontal) layersealant body preventing or minimizing bypass of the liquid propellant.The second composition has a density of 0.9-1.5 g/cm³ and the thirdcomposition has a density of 0.8-1.2 g/cm³. The fourth and fifthcompositions isolate the third composition from the liquid propellant.Respective densities are 1.0-1.8 g/cm³ and 0.8-1.2 g/cm³. The sixthcomposition is a gel sealant, whose purpose is to temporarily seal thepig train from the rear upon launch. It has a density of 0.8-1.2 g/cm³.

Reference is now made to FIG. 2, which is a simplified flow chart of amethod 200 for sealing a pipeline, in accordance with an embodiment ofthe present invention, with reference to FIG. 1A. A sealant composition,such as sealant composition 102 is introduced to pipeline 106 in asealant composition introducing step 202. This may be performed from oneend of the pipe, from a fire hydrant, from a manhole, vertical, lateralpipe, communication pipe or branch pipe.

Thereafter, gel pig 104 is introduced from the same end of the pipe asthe sealant composition or from a manhole or vertical, in a gel pigcomposition introducing step 202.

The combination of the sealant composition 102 and gel pig 104 is termedherein a “pig train”. The pig train travels along the pipe in atravelling step 206 to site 108 of the leakage. The sealant compositionis operative to seal the leakage in a sealing step 208. It typicallytakes a few minutes to several hours until the seal is fully cured.

Typically, gel pig 104 or any of the other gel pigs described herein isof approximately the same diameter as the inner diameter of the pipe andis typically 0.5-10 diameters in length. The physical properties of thegel pig appear in Table 4.

Reference is now made to FIG. 3, which is a simplified flow chart ofanother method 300 for sealing a pipeline, in accordance with anembodiment of the present invention, with reference to FIG. 1.

A first gel pig 114 is introduced to the pipe from a fire hydrant, froma manhole, vertical, lateral pipe, communication pipe or from a branchpipe in an introducing pig step 302.

A sealant composition, such as sealant composition 102 is introduced topipeline 106 in a sealant composition introducing step 304. This may beperformed from one end of the pipe or from a manhole or vertical.

Thereafter, a second gel pig 104 is introduced from the same end of thepipe as the sealant composition or from a manhole or vertical, in asecond gel pig composition introducing step 306.

The combination of the sealants composition 102 and gel pigs 114, 104 orany of the other gel pigs described herein, is termed herein a “pigtrain”. The pig train travels along the pipe in a travelling step 308 tosite 108 of the leakage. The sealant composition is operative to sealthe leakage in a sealing step 310. It typically takes a few minutes toseveral hours until the seal is fully cured.

Typically, gel pigs 104, 114 are of approximately the same diameter asthe inner diameter of the pipe and is typically 0.5-10 diameters inlength. The physical properties of the front gel pig 114 appear in Table5.

The pig train is typically recovered from the pipeline in an exit pipestep 312.

FIG. 4 is a simplified flow chart of another method 400 for sealing apipeline, in accordance with an embodiment of the present invention,with reference to FIG. 1C.

A first gel pig 118 is introduced to the pipe from a fire hydrant, froma manhole, vertical, lateral pipe, communication pipe or from a branchpipe in a first introducing pig step 402.

A sealant composition, such as sealant composition 116 is introduced topipeline 106 in a first sealant composition introducing step 404. Thismay be performed from one end of the pipe or from a manhole or vertical.

Thereafter, a second gel pig 114 is introduced from the same end of thepipe as the first sealant composition or from a manhole or vertical, ina second gel pig composition introducing step 406.

A second sealant composition, such as sealant composition 102 isintroduced to pipeline 106 in a second sealant composition introducingstep 408. This may be performed from one end of the pipe or from amanhole or vertical.

Thereafter, a third gel pig 104 is introduced from the same end of thepipe as the first and second sealant composition or from a manhole orvertical, in a third gel pig composition introducing step 410.

The combination of the sealants compositions 102, 116 and gel pigs 118,114 and 104 is termed herein a “pig train”. The pig train travels alongthe pipe in a travelling step 412 to site 108 of the leakage. Thesealant composition(s) is/are operative to seal the leakage in a sealingstep 414. It typically takes a few minutes to several hours until theseal is fully cured.

Typically, gel pigs 104, 114, 118 are of approximately the same diameteras the inner diameter of the pipe and is typically 0.5-10 diameters inlength. The physical properties of the front/middle gel pig 118/114appear in Table 5.

The pig train is typically recovered from the pipeline in an exit pipestep 416. In some cases, one or more of the gel pigs may be replacedwith a polymer pig, such as polyurethane.

Reference is now made to FIG. 5, which is a simplified pictorialillustration showing a system 500 for sealing a pipeline, in accordancewith an embodiment of the present invention.

System 500 comprises a front gel pig 114 and a real gel pig 104. Asealant composition 102 is disposed between pigs 114 and 104, forming apig train 120. A fluid 502 is inserted to a pipeline 501 and a firstpressure P₁ 506 is applied to fluid 502. Additionally a secondcounter-pressure P₂, 508 is applied to a second fluid 504. Typically P₁is greater than P₂. The average velocity of pig train 120 is determinedby the fluid properties, the smoothness of the pipe interior and apressure difference (P₁−P₂).

Pressure P1 is introduced by a pump 512, pressure from an existingnetwork or any other suitable pressure introducing means, known in theart. The pressure P1 is typically regulated by control means, as areknown in the art.

Pressure P2 may be introduced by any suitable passive means, such as apressure relief valve 514, a discharge valve, a pressure regulator orthe like.

The gel pigs of the present invention provide the following advantages:—

-   -   1) Gel pigs are adapted to multi-dimensioned pipes-adaption to        variable and changing diameters in situ.    -   2) Non-abrasive very non-abrasive (in contrast to poly pigs,        which may get stuck in a pipeline, induce a reddening of water,        induce a change of pH of the water, or may abrade tubicles).    -   3) Gel pigs of the present invention are to introduce into pipe        and to remove from pips providing system flexibility.    -   4) Gel pigs of the present invention do not normally get stuck        in the pipe (better than polymer (solid) pigs) and due to their        fluidity, can always be flushed out.    -   5) The rear pig does not compromise/dislodge/disengage newly        formed seals, in contrast to solid pigs.    -   6) Gel pigs of the present invention are fully flushable (in        contrast solid pigs leave debris).    -   7) A front pig of the present invention allows water to bypass        and overtake-allows escape route to prevent/minimize sealant        composition dilution.    -   8) In a two pig system, the rear pig acts differently to the        front pig.    -   9) Pig receiver/retriever for solid pigs is not required for gel        pigs.    -   10) The gel pigs of the present invention are biodegradable.    -   11) Gel pigs of the present invention require reduced        transportation costs—here can be formulated at/near the site of        use. Saving on transport costs.

EXAMPLES Example 1

A gel pig is formed according to the following method.

-   -   1) Chemical constituents were obtained in accordance with table        1.    -   2) A gel pig mixture was made by mixing the components of table        1 in a stirred vessel for several (1-30) minutes at ambient        temperature and pressure.    -   3) The resultant gel formed was stored in a closed container in        the dark for 0-60 days at room temperature before use.

TABLE 1 Chemical composition of gel pig Functional Example ComponentConstituent Weight percent [%] Hygroscopic Cellulose, gum,  1-10component gelatin or other surfactant Oil or other 0-8 Base Aluminum 0-20 hydroxide Particulate Silica 0-2 Carrier fluid Water 70-95 Total100

According to some embodiments, the physical properties of the gel pigsappear as in tables 2 and/or 3.

According to one or more embodiments, hydrophobic solvents are liquidoils originating from vegetable, marine or animal sources. The canolaoil exemplified may be replaced by any suitable liquid oil includingsaturated, unsaturated or polyunsaturated oils. By way of example, theunsaturated oil may be olive oil, corn oil, soybean oil, cottonseed oil,coconut oil, sesame oil, sunflower oil, borage seed oil, syzigiumaromaticum oil, hempseed oil, herring oil, cod-liver oil, canola oil,salmon oil, flaxseed oil, wheat germ oil, evening primrose oils ormixtures thereof, in any proportion.

According to one or more embodiments, the silica exemplified may bereplaced by a) microsponges, b) silica, c) mineral bodies like zeolite,bentonite, (iii) graphite, including polymers, dendrimers and liposomes,or mixtures thereof, in any proportion.

According to one or more embodiments, the aluminum hydroxide exemplifiedmay be replaced by minerals such as aluminum phosphate and calciumphosphate or mixtures thereof, in any proportion.

According to one or more embodiments, the hydroxyethyl celluloseexemplified may be replaced by any at least one polymeric additiveselected from the group consisting of polysaccharides, naturalpolysaccharides, derivatives thereof, modified polysaccharides,derivatives thereof, starch, dextrin, glycogen, cellulose and chitin,glycosaminoglycans (GAG's), chondroitin sulphate, dermatan sulphate,keratan sulphate, heparan sulphate, heparin, and hyaluronan, amylose andamylopectin, cellulose derivatives, xanthan gum, sodium CMC,methylcellulose, and hydroxyl propyl methyl cellulose or mixturesthereof, in any proportion.

Specific non limiting examples of surfactants are an ionic surfactant, anon-ionic surfactant, a hydrophobic surfactant or mixtures thereof, inany proportion.

Exemplary hygroscopic agents that can be used in accordance with one ormore embodiments include, for example, naturally-occurring polymericmaterials, such as locust bean gum, sodium alginate, sodium caseinate,egg albumin, gelatin agar, carrageenan gum, sodium alginate, xanthangum, quince seed extract, tragacanth gum, guar gum, starch, chemicallymodified starches and the like, semi-synthetic polymeric materials suchas cellulose ethers (e.g. hydroxyethyl cellulose, methyl cellulose,carboxymethyl cellulose, hydroxy propylmethyl cellulose), guar gum,hydroxypropyl guar gum, soluble starch, cationic celluloses, cationicguars, and the like, and synthetic polymeric materials, such ascarboxyvinyl polymers, polyvinylpyrrolidone, polyvinyl alcohol,polyacrylic acid polymers, polymethacrylic acid polymers, polyvinylacetate polymers, polyvinyl chloride polymers, polyvinylidene chloridepolymers and the like. Mixtures of the above compounds are contemplated.

According to some further embodiments, a base may be selected fromsodium hydroxide, magnesium hydroxide, aluminum hydroxide, potassiumhydroxide and combinations thereof.

TABLE 2 Physical and Chemical properties of rear gel pig minimum maximumViscosity cPs 5 10000 Density g/cm³ 0.8 1.2

TABLE 3 Physical and Chemical properties of front gel pig minimummaximum Viscosity cPs 5 10000 Density g/cm³ 0.8 1.5

The references cited herein teach many principles that are applicable tothe present invention. Therefore the full contents of these publicationsare incorporated by reference herein where appropriate for teachings ofadditional or alternative details, features and/or technical background.

It is to be understood that the invention is not limited in itsapplication to the details set forth in the description contained hereinor illustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Those skilled in the art will readily appreciate that variousmodifications and changes can be applied to the embodiments of theinvention as hereinbefore described without departing from its scope,defined in and by the appended claims.

The invention claimed is:
 1. A method for curing at one leakage site ina pipeline, the method comprising a. introducing a pig train into thepipeline, the pig train comprising: i) at least one gel pig comprising:a) a hygroscopic component in a concentration of 1-10% w/w; b) asurfactant in a concentration of 0 to 10%; c) water in a concentrationof 85-95% w/w; and d) a base in a concentration of 0-10%; and ii) atleast one sealant composition comprising: e) at least one filler; f) atleast one gelling agent; and g) at least one aqueous agent; wherein saidat least one gel pig and said at least one sealant composition form saidpig train; b. enabling said pig train to move along said pipeline to aregion of said at least one leakage and to seal said at least oneleakage.
 2. A method according to claim 1, wherein said at least one gelpig comprises one gel pig and said at least one sealant compositioncomprises one sealant composition.
 3. A method according to claim 2,wherein said at least one gel pig comprises one rear pig.
 4. A methodaccording to claim 1, wherein said at least one gel pig comprises twogel pigs and said at least one sealant composition comprises one sealantcomposition.
 5. A method according to claim 1, wherein said at least onegel pig comprises three gel pigs and said at least one sealantcomposition comprises two sealant compositions.
 6. A method according toclaim 1, wherein said pig train moves along said pipeline at a speed of0.01 to 10 m/s.
 7. A method according to claim 1, wherein said at leastone gel pig further comprises an oil.
 8. A method according to claim 1,wherein said at least one gel pig comprises a rear pig and a front pigof different compositions.
 9. A method according to claim 8, whereinsaid inner profile of said pipeline is reduced in diameter in at leastone section by at least 20%.
 10. A method according to claim 9, whereinsaid pressurized fluid is at a pressure of 1-150 bar.
 11. A methodaccording to claim 9, further comprising counter-pressurizing said pigtrain from a second end of said pipeline with a counter pressurizedfluid.
 12. A method according to claim 11, wherein said counterpressurized fluid is for controlling velocity of movement of said pigtrain along said pipeline.
 13. A method according to claim 1, furthercomprising propelling a pressurized fluid from a first end thereof alongsaid pipeline.
 14. A method according to claim 1, wherein said pig trainprevents a bypass of a propelling product by more than 30%.
 15. A methodaccording to claim 1, further comprising extracting said pig train fromsaid pipeline via a conduit of less than two inch diameter at a pressureof less than 3 bar.
 16. A method according to claim 1, wherein said pigtrain is launched from a pipe of a diameter of less than 50% of saidpipeline.